1. Field of the Invention
The present invention relates to a coating apparatus and method for applying a chemical liquid, such as a resist, onto a substrate, such as a semiconductor wafer. The present invention also relates to a coating/developing apparatus including the coating apparatus and a storage medium that stores a program for executing the coating method.
2. Description of the Related Art
In the process of manufacturing semiconductor devices, there is a step of applying a coating liquid onto a substrate by a spin coating method. The coating liquid may be exemplified by a resist, a chemical liquid for forming an anti-reflection film, and a chemical liquid containing a precursor of silicon oxide for forming an insulating film. The spin coating method is arranged to use a spin chuck to attract and hold the back side central portion of a substrate, such as a semiconductor wafer (which may be simply referred to as “wafer”) or a LCD glass substrate. The coating liquid is supplied on the front side central portion of the substrate, and the spin chuck is rotated about a vertical axis, so that the coating liquid is spread toward the peripheral portion of the substrate or wafer by a centrifugal force.
Incidentally, due to aggravation of environmental issues, it is required to reduce consumption of organic solvents and emission thereof into the atmosphere. Under the circumstances, for example, in resist coating apparatuses for performing a spin coating method as described above, a resist-saving coating method may be used to reduce resist consumption, such that an organic solvent is first supplied onto a wafer to improve the compatibility of the wafer with a resist, and then the resist is supplied onto the wafer. According to this resist-saving coating method, consumption of an organic solvent contained in the resist becomes smaller due to a decrease in resist consumption, whereby the total amount of the organic solvent used for forming a film per wafer is reduced.
However, where a resist film R is formed by spin coating as described above, a resist supplied onto the wafer W is scattered as mist M, and the scattered mist M may be deposited on the back side peripheral portion of the wafer W, as shown in FIG. 24A. In order to prevent this mist M from becoming particles and thereby hindering the normal resist pattern formation, there is adopted a step of supplying a solvent, such as a thinner, onto the back side of the wafer W from a back side cleaning nozzle 11 to wash out the mist M, as shown in FIG. 24B.
This back side cleaning step using the back side cleaning nozzle 11 may consume the largest amount of solvent among steps performed in a coating/developing apparatus including a resist coating apparatus, such as 20 cc of solvent per wafer. Where coating and developing processes are performed on 600 wafers per month in the coating/developing apparatus and the solvent is consumed by 20 cc per wafer for the purpose described above, the total amount of consumption of the solvent reaches 120 tons per month in the resist coating apparatus. The explanation described above concerns a resist coating apparatus, but back side cleaning may be performed, as in resist film formation modules, in other various apparatuses for applying a chemical liquid onto a substrate to form a film of the chemical liquid. Accordingly, consumption of organic solvents for such back side cleaning is a problematic issue.
In order to prevent a liquid from being scattered, spin coating is performed in a cup with a suction passage connected thereto at a lower side, and the interior of the cup is exhausted by suction through the suction passage to form exhaust flows inside the cup. In this respect, studies have been made to alter the structure of the cup to control the exhaust flows, so that deposition of mist M on the wafer W is decreased. However, in this case, deposition of mist cannot be completely prevented, and so the solvent consumption for back side cleaning is still not so small. Rather than this method, there is a case where a larger amount of solvent than before is used to wash out mist to reliably prevent particle contamination. Jpn. Pat. Appln. KOKAI Publication No. 2-16447 (FIG. 1) discloses a coating apparatus arranged to perform resist coating on a wafer in a floating state, but this apparatus cannot solve the problem described above.